**3.3 Experiment**

We performed three experiments and calculations using the same control parameter conditions. **Table 4** lists the airflow control parameters of (1) angle (°), (2)

*Application of CFD to Prediction of Heat Exchanger Temperature and Indoor Airflow Control… DOI: http://dx.doi.org/10.5772/intechopen.110076*


#### **Table 4.**

*Specification of CFD. Boundary condition for air outlet.*

volume rate (m3 /min), and (3) temperature (°C). Angle is defined as the measurement between the horizontal line and the airflow direction.

#### **3.4 Result**

In the experiment of **Table 4**, tests (A) and (B) resulted in short airflow circulation. Test (C) resulted in long airflow circulation. We compared the tip of blowing airflow to verify the numerical results.

#### *3.4.1 Short airflow circulation control*

**Figure 14** compares the airflow tips of tests (A) and (B) with the temperature contour plots at the center of the room. The calculated results are 180 seconds after the initial condition for both (A) and (B). The initial temperature of the indoor air was set to 24 °C and the initial temperature of the wall was 24 °C. Under the conditions of test (A), the blowing airflow floated in the center of the room and did not reach the floor in both experiments and values. However, the distance traveled by the tip of the blowing airflow was different (experimental, 3.6 m; numerical, 2.0 m). Under test (B) conditions, both experimental and numerical airflows contacted the floor; moreover, the distance of the tip of both experimental and numerical airflows was 3.6 (m).

#### **Figure 14.**

*Indoor airflow experiment and calculation. Comparison of test (A): Both experimental and numerical blowing warm airflow floated in the middle of the room, but the distance traveled by the tip of warm airflow was different. Comparison of test (B): Both experimental and numerical airflow touched the floor*.

#### *3.4.2 Long airflow circulation control*

**Figure 15** shows the results with test (C) conditions. **Figure 15a** visualized measured temperature by experimental thermocouples position. **Figure 15b** is the numerical simulation result of test (C) condition. The initial temperature of the room air was 20 °C, and the initial temperature of the walls was 10 °C. The contour plot is 180 seconds after the initial condition. Under the test (C) conditions, the both experimental and numerical results were such that the blowing airflow reached the floor and the tip of the blowing airflow reached the wall opposite where the room air conditioner was installed.

**Figure 16** is three-dimensional isosurface of temperature at 26 °C. In the experiment, the temperature isosurface of 26 °C is limited to the floor, but in the calculation, it reaches the opposite side of the wall where the air conditioner is installed and the isosurface of 26 °C covers the half of the ceiling. In this model, the amount of heat leakage is simulated by using the initial temperature of the room walls as a parameter. This method can adjust the heat balance between the room air and the room walls, but it cannot simulate the airflow from air gaps. In test (C), blowing airflow travels along walls, such as floor and ceiling surfaces. The area where airflow flows along the wall surface in test (C) is larger than that of tests (A) and (B). It is possible that the airflow gaps on the wall surfaces in the test (C) are larger than in tests (A) and (B).

The positions of the arrival of the blowing airflow could be predicted by the calculation model, but the absolute values of the temperature distribution differed between the calculations and experiments.

*Indoor airflow experiment. Comparison of test (A): Both experimental and numerical blowing warm airflow reached the back wall of the room.*

**Figure 16.**

*Indoor airflow experiment and calculation of test (C). The temperature of isosurface is plotted at 26 °C.*

*Application of CFD to Prediction of Heat Exchanger Temperature and Indoor Airflow Control… DOI: http://dx.doi.org/10.5772/intechopen.110076*

When calculations are used as a surrogate model for experiments, it is necessary to analyze the calculation results, taking into account the differences in absolute values of temperature.

We found some differences in the experiments and calculations; however, qualitatively, the airflow calculations are similar to the experiments. The ability to compare experiments and calculations has enabled us to know the difference between experimental and calculated results. By knowing the difference, the number of experiments can be reduced by calculation, thereby reducing the cost of designing airflow control.
